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Old 05-30-2008, 05:14 AM   #1
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Regenerate your AC?

This is a follow up and an expansion on my thread about alternators in the "experiments" forum..

After thinking about it for a while, it occurs to me that if you had a circuit that would only allow the AC compressor to engage during deceleration fuel cut off that you could regenerate almost all of your AC energy in city type driving..

Perhaps a reservoir for compressed freon.

A small microcontroller that reads injector pulse width and triggers a relay would take care of the control logic.

Wouldn't it be nice to cool your car in the middle of the summer with energy you were going to have to throw away by decelerating anyway?

Hook the alternator to the same microcontroller and produce the power for your blower/fans/accessories mostly from regenerated power too.
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Old 05-30-2008, 05:34 AM   #2
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logical reasoning.... wouldn't work on my specific car, since the GP disengages the slushbox at speeds under 60mph during coasting. But for manuals, I could see the in gear slowdown help. I'm sure someone will see it as counter-intuitive and it may not actually produce the desired results (higher FE). But hey, if you're in fuel cut, it wouldn't waste anymore fuel than if the AC was off.

lots of quirky ideas that only testing will tell if they produce the desired results.
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Old 05-30-2008, 05:54 AM   #3
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Nice idea. Should make it work such that when the AC is off, accumulated pressure drives the compressor for an extra .5-1HP at takeoff.

Actually, I wonder if the alternator decel regeneration thing would work better with an "accumulator", meaning a small deep cycle battery, maybe a big capacitor. Reason is because ECUs manage field current and battery charge pretty well... and if your main battery is charged, you can't really "do anything" with the decel energy... so an accessory storage device to dump the energy to, and bleed off into the main battery as necessary might work. Basically, you'd intercept when the ECU was increasing field current on the alternator, and leave it off, switching in the secondary battery or capacitor until it had satisfied the extra load or was depleted, then switching back on the field current when you'd used that up.

Or you could just leave that system separate from the service electrics, and regen to a battery that you'd tap for HHO etc, or do your own mild hybrid thing.
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Old 05-30-2008, 06:40 AM   #4
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Actually, I wonder if the alternator decel regeneration thing would work better with an "accumulator", meaning a small deep cycle battery, maybe a big capacitor.
Your regular battery works fine if you strictly limit charging to dfco once the engine has warmed up. If you only charge during dfco then you recycle a nice percentage of regen energy.

As for the rest of it, put a clutch on the crankshaft pulley and design a controller for your alternator to work it as a motor as well and you could do a mild hybrid that would work well for p and g. The more battery you put in, the more hybrid effect you could use.

Battery technology is improving so any hybridizing you do today becomes more efficient over time if you upgrade your batteries.
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Old 05-30-2008, 06:52 AM   #5
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Originally Posted by almightybmw View Post
logical reasoning.... wouldn't work on my specific car, since the GP disengages the slushbox at speeds under 60mph during coasting.
That's interesting, I didn't know there were any cars that still did that.
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Old 05-30-2008, 07:08 AM   #6
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Quote:
Originally Posted by almightybmw View Post
logical reasoning.... wouldn't work on my specific car, since the GP disengages the slushbox at speeds under 60mph during coasting.
Are you sure about that? Have you tried changing to neutral and watching the tach? My GMC probably unlocks the TC but still has a slight amount of engine braking, and occasionally hits DFCO during long coasts in Drive.

Direct monitoring of fuel injectors is way cool.

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But hey, if you're in fuel cut, it wouldn't waste anymore fuel than if the AC was off.
...but it would waste energy by slowing the car more. Since you're inentionally slowing anyway, sounds great to me. The only problem for me would be that it wouldn't be cold enough. By the time it's hot enough for me to prefer A/C over open windows, I need it on its maximum setting for the whole ride, unless I'm just using it to avoid wind noise instead.
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Old 05-30-2008, 07:16 AM   #7
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The only problem for me would be that it wouldn't be cold enough. By the time it's hot enough for me to prefer A/C over open windows, I need it on its maximum setting for the whole ride, unless I'm just using it to avoid wind noise instead.
Are you sure the AC compressor runs all the time?
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Old 05-30-2008, 07:40 AM   #8
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Originally Posted by fumesucker View Post
Are you sure the AC compressor runs all the time?
It's not the car, it's me. It doesn't matter WHAT I'm driving or whether the compressor is running (and I usually have it set to "Max A/C" and temp at coldest). By the time the weather is like that, it's just not possible for me to be cool enough; a few minutes in 90?F/80% humidity makes me uncomfortably hot for hours even if I spend those hours in 60?F.

I'm generally warmer than others. I wear sandals all year, even while shoveling snow (my feet are the worst offenders with being excessively warm), and I wear shorts + T-shirt when others are still in jeans and jackets. At work I'm happy that I have my own small office with a window air conditioner that I control, and another window where I can have a fan blowing on me if it's not hot enough for A/C. Still I have to kick off my shoes under my desk all day.
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Old 05-30-2008, 08:06 AM   #9
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By the time it's hot enough for me to prefer A/C over open windows, I need it on its maximum setting for the whole ride, unless I'm just using it to avoid wind noise instead.
That's kinda like me too, I can cope with mid 30s dry heat, but as soon as humidex gets into mid 30s, I need the AC on, and it's usually gonna have to work real hard to keep up by then.

Keep looking out for one of those windshield covers that's extra long, so you could throw it over on the outside, and keep the sun off the vent/cowl, since the blower will fry you for 10 minutes if you've left it standing in the sun sometimes. Probably heat soaks from the engine bay too though, maybe I'll think about how to get some insulation in there.
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Old 05-30-2008, 01:18 PM   #10
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Just because the blower is on and cold air is coming out does not mean the compressor is always engaged. AC systems usually won't let the evaporator end get too cold, ice tends to form and then blocks the air flow.
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